Numerous attempts have been made to achieve golf balls endowed with both increased carry and a good feel when hit. The approach most commonly taken in solid golf balls has been to alter the hardnesses of the cover and the core.
For example, JP-A 23069/1994 discloses a solid golf ball having a three-layer construction comprising an inner core layer, an outer core layer, and a cover wherein the inner core layer has a diameter of 23 to 35 mm and a Shore D hardness of 30 to 60 and the outer core layer has a Shore D hardness of 30 to 56 As a result a suitable spin is maintained and the rebound characteristics and carry are improved. However, when this solid golf ball is hit at a relatively low head speed of about 35 m/s, the ball is given a low initial velocity, failing to have sufficient carry.
JP-A 170012/1994 describes a solid golf ball in which the inner core layer is made of Surlyn, commonly used as a cover material, that has been foamed (.rho.=0.2 to 1.0). Yet, the inner core layer is so soft that the ball provides a poor rebound and an inadequate carry.
Because most conventional golf balls are targeted at professional golfers and skilled amateurs, they have been designed for optimal performance in a relatively high head speed range of about 40 to 45 m/s. But these golf balls are often less than ideal for use by relatively low head speed players such as women golfers and seniors who strike the ball at head speeds of less than 40 m/s. If a low head speed golfer plays a shot with a driver, for instance, the speed upon impact (initial velocity) conventional balls acquire will be too low to provide an adequate carry.